I think this will fix the issue if you have SSL enabled:
Setting uploadReadAheadSize in applicationHost.config file on IIS7.5 would resolve your issue in both cases. You can modify this value directly in applicationhost.config.
Select the site under Default Web Site
Select Configuration Editor
Within Section Dropdown, select “system.webServer/serverRuntime”
Enter a higher value for “uploadReadAheadSize” such as 1048576 bytes. Default is 49152 bytes.
During client renegotiation process, the request entity body must be preloaded using SSL preload. SSL preload will use the value of the UploadReadAheadSize metabase property, which is used for ISAPI extensions
Reference.
I got it working by doing the following
Go to IIS.
Click on the server name
In the features (icons), chose the configuration editor.
Click on the dropdowns on the top with Settings
Traverse the path system.webServer -> security -> requestFiltering -> maxAllowedContentLength and set it to 334217728. (Then hit enter and then apply on the top right).
You can also restart the webserver for good measure.
After that I could upload my 150k database to phpymyadmin.
I also set post_max size to 8000 in php.ini in programs/PHP/phpversion/php.ini
It may be overkill for the sizes but it gets the job done when you’ve got big files.